1. Field of the Invention
The present invention relates to an asynchronous transfer mode (ATM) based delay adaptive scheduling apparatus adaptive according to traffic types and method thereof, and more particularly to an ATM-based delay adaptive scheduling apparatus that is adaptive to a delay time generated at an exchange node based on traffic characteristics and quality of service (QoS) provided in a traffic setting step, and a method thereof. The present invention is based on Korean Patent Application 2001-36013 filed on Jun. 23, 2001, which is incorporated herein by reference.
2. Description of the Related Art
With technological developments in high speed switching and optical transmission fields, data transmission at high speed and wideband service at a speed ranging from several hundred Mbps to several dozens of Gbps were enabled. Meanwhile, a broadband integrated services digital network (B-ISDN) based on an asynchronous transfer mode (ATM) provides wideband multi-media services including video on demand (VOD), video conference, etc.
One of the most important preconditions for supporting the wideband multi-media services in terms of network design is to guarantee bandwidth sufficient for efficient provision of services. Further, for a network provider and a user, use of bandwidth has to be optimized during initial connection in the network as constructed. Accordingly, there will be an agreement between the provider and the user for a proper QoS for each traffic type, and here, an average delay becomes an essential factor that determines conditions for QoS demand. Accordingly, importance of a delay boundary at an intermediary node is emphasized.
For an ATM network, various algorithms have been suggested, like a scheduling algorithm for reallocating the bandwidth according to demands of respective sources, and an algorithm that is fast, efficient, and suitable for limited performance. References can be found in “A service architecture for ATM: from application to scheduling, IEEE network, pp. 6–14, May/June 1996” by Mark W. Garrett, and “Start-time fair queuing: A scheduling algorithm for integrated services packet switching networking, Vol. 5, No. 5, pp. 690–704, October 1997” by Pawan Goyal, Harrick M. Vin, and Haichen Cheng on the field of IEEE/ACM networking.
Most algorithms, however, cannot distinguish traffic sensitive to time during scheduling from traffic sensitive to damage. Accordingly, a delay boundary between end points required by the traffic sensitive to time, cannot be guaranteed. In order to guarantee the delay boundary between the end points as required by the traffic sensitive to time, there occurs a waste of bandwidth. This problem is specified in a doctorate thesis titled “Research on an efficient operation of a port of an output buffer type ATM switch” (Dr. Ho-yong Ryu. PhD. Dissertation. Kwangwoon University. 1998. A duplicated copy obtainable from the library of Kwangwoon University).
The algorithm like fair queuing (FQ) that is operated by a round-robin scheduling has a drawback that it could not provide different bandwidths for respective sources. Suggestions to solve this problem are: weighted fair queuing (SFQ) and a generalized processing sharing (GPS). References to the SFQ and GPS can be found in “Design of a weighted fair queuing cell scheduler for ATM network, IEEE Globelcom98, Vol. 1, pp. 405–410, November 1998” contributed by Yuhua Chen and Jonathan S. Turner on the IEEE Globelcom, and the “Bandwidth allocation of r-multiple qualities of service using generalized processor sharing, IEEE transactions on information theory, Vol. 42, No. 1, pp. 268–272, January 1996” by G. De Veciana and George Kesidis.
In the input queuing switching system using the above queuing model, however, output conflict and head of line blocking cause delay between end points and subsequent reduction of processing ratio. Further, in the multi-traffic conditions, in order to ensure QoS for the respective traffic types, ATM forum TM 4.0 allocates a priority to each traffic type, and the priority serves as an important reference to determine the order of transmission during the scheduling process.
FIG. 1 is a view showing the structure of a system for a conventional input buffering type crossbar relaying algorithm.
Referring to FIG. 1, when a cell arrives at one of the input ends (100a through 100n), a shaper 110 applies the traffic characteristic of the input cell into a predetermined traffic type. A crossbar scheduler 120 determines whether to provide service or not based on the priority determined in accordance with the traffic type of the input cell. A crossbar switching fabric 130 transmits the cell to a corresponding output end (140a through 140n), and accordingly, the cell is transmitted through the corresponding output end (140a through 140n).
FIG. 2 shows an order of transmission of each cell input in the system for the conventional input buffering type crossbar relaying algorithm. When the cells shown in FIG. 2 are in queue, regardless of service finish time preset for each cell, the cells are serviced by an order of constant bit rate (CBR), real-time variable bit rate (rt-VBR), non-real time variable bit rate (nrt-VBR), available bit rate (ABR), and unspecified bit rate (UBR). Accordingly, the low priority cells are waiting in queue until the higher priority cells are serviced, resulting in a waste of available bandwidths.